The proposed studies deal with the small nuclear ribonucleoproteins (snRNPs) in animal cell nuclei, particularly their organization into macromolecular complexes and larger aggregates visible by conventional light microscopy. snRNPs are an essential part of the nuclear machinery that prepares RNA molecules for export from the nucleus to the cytoplasm - the conversion of pre-messenger (pre-mRNA) molecules to the functional messengers (mRNA). A great deal is known about the biochemical reactions in which snRNPs are involved, primarily the process of splicing, which involves the removal of specific intron sequences from the pre-mRNA and the accurate joining of the remaining pieces. However, the distribution of snRNPs within the nucleus is not well understood. Studies on the giant nuclei of amphibian oocytes show that snRNPs are associated with the pre- mRNA molecules on the chromosomes, as one would expect, but they are also abundant in thousands of nuclear bodies known as snurposomes. The snurposomes may be sites for assembly of snRNPs pinto macromolecular complexes that are then transported to the chromosomes, where they actually function. The proposed studies will characterize the snurposomes of insect oocytes using immunofluorescence to identify the protein components and in situ hybridization to recognize specific snRNA molecules. Based on composition and morphology, several different classes of snurposomes are recognizable in amphibian oocytes, and similar heterogeneity is anticipated in insects. The RNA processing steps in which snRNPs are involved concern the most general and important biochemical reactions within cells. Not only is correct RNA processing essential to normal cell function, but the same biochemical machinery is used by viruses when they infect cells. Thus, knowledge about snRNPs in various cell types has important implications for both normal and diseased cells.